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Zero-Voltage Switch with adjustable Ramp
U217B
Description
The integrated circuit, U217B, is designed as a zero-
voltage switch in bipolar technology. It is used to control
resistive loads at mains by a triac in zero-crossing mode.
A ramp generator allows power control function by
period group control, whereas full-wave logic guarantees
that full mains cycles are used for load switching.
Features
D Direct supply from the mains
D Current consumption 0.5 mA
D Very few external components
D Full-wave drive – no DC current component in the
load circuit
D Negative output current pulse typ. 100 mA –
short-circuit protected
D Simple power control
D Ramp generator
D Reference voltage
Applications
D Full-wave power control
D Temperature regulation
D Power blinking switch
Block Diagram
220 kW R2
(250 V~) (Rsync)
D1 BYT86/800
R1
18 kW/
2W
Load
1000 W
L
C2
2.2 mF/
10 V
R4
100 kW
R5
15 kW
max
100 kW
min
R6
58 kW
2
1 Ramp
generator
8
Synchronization
3
+
4+
Full-wave logic
Comparator
5
Supply
7
GND
C1
100 mF/
16 V
TIC
236N
VM =
230 V~
MT2
6
Pulse
amplifier
100 W
MT1
R3 G
Reference voltage
1.25 V
U217B
N
Figure 1. Block diagram with typical circuit, period group control 0 to 100%
Order Information
Extended Type Number
U217B-x
U217B-xFP
U217B-xFPG3
Package
DIP8
SO8
SO8
Remarks
Tube
Tube
Taped and reeled
Rev. A4, 23-Feb-01
1 (11)

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U217B
Pin Description
Ramp 1
8 Vsync
U217B
CRamp 2
OP+ 3
U217B
7 GND
6 Output
OP– 4
5 VS
1
–VS
Ramp
control
2 C2
Figure 2. Pinning
Figure 3. Pin 1 internal network
Pin Symbol
Function
1 Ramp Ramp output
2 CRAmp Ramp capacitor
3 OP+ OP non-inverting input
4 OP– OP inverting input
5 VS Supply voltage
6 Output Trigger pulse output
7 GND Ground
8 Vsync Voltage synchronization
General Description
V1
1.4 V
t
Final voltage
Vmin
7.3 V
Initial voltage
T Vmax
–VS(Pin5)
Figure 4. Threshold voltage of the ramp
The integrated circuit U217B is a triac controller for zero-
crossing mode. It is designed to control power in
switching resistive loads of mains supplies.
Information regarding supply sync. is provided at Pin 8
via resistor RSync.
To avoid DC load on the mains, the full-wave logic
guarantees that complete mains cycles are used for load
switching.
A fire pulse is released when the inverted input of the
comparator is negative (Pin 4) with respect to the
non–inverted input (Pin 3) and internal reference voltage.
A ramp generator with free selectable duration can be
performed by capacitor C2 at Pin 2. The ramp function is
used for open-loop control (figure 4), but also for applica-
tion with proportional band regulation (figure 11). Ramp
voltage available at capacitor C2 is decoupled across the
emitter follower at Pin l. To maintain the lamp flicker
specification, ramp duration is adjusted according to the
controlling load. In practice, interference should be
avoided (temperature control). Therefore, a two-point
control is preferred to proportional control. One can use
internal reference voltage for simple applications. In that
case, Pin 3 is inactive and connected to Pin 7 (GND), see
figure 13.
Triac Firing Current (Pulse)
This depends on the triac requirement. It can be limited
with gate series resistance which is calculated as follows:
RGmax 
7.5 V – VGmax
IGmax
– 36 W
IP = IGmax
T
tp
where:
VG = Gate voltage
IGmax = Maximum gate current
Ip = Average gate current
tp = Firing pulse width
T = Mains period duration
Firing Pulse Width tp (Figure 5)
This depends on the latching current of the triac and its
load current. The firing pulse width is determined by the
zero-crossing identification which can be influenced with
the help of sync. resistance, Rsync, (figure 6).
tp =
2
arc. sin
IL
VM
w P Ǹ2
2 (11)
Rev. A4, 23-Feb-01

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U217B
whereby:
IL =
VM =
P=
Latching current of the triac
Mains supply, effective
Power load (user’s power)
Total current consumption is influenced by the firing
pulse width which can be calculated as follows:
Rsync
+
VM
Ǹ2
sin
3.5
(w
tp
2
)–0.6
10–5A
V
–49
kW
10.00
Vmains = 230 V
1.00
The series resistance R1 can be calculated (figures 7
and 8) as follows:
R1max = 0.85
Vmin – VSmax
2 Itot
; P(R1) =
(VM – VS)2
2 R1
Itot = IS + IP + Ix
whereby:
VM = Mains voltage
VS = Limiting voltage of the IC
Itot = Total current consumption
IS = Current requirement of the IC (without load)
Ix = Current requirement of other peripheral
components
P(R1) = Power dissipation at R1
0.10
0.01
10
IL ( mA)
200
100
50
100 1000
P(W)
10000
Figure 5. Output pulse width
50
40
30
20
10
VMains=230VX
3600
3200
2800
2400
2000
1600
1200
800
400
0
0
200 400 600 800 1000 1200
tp
Figure 6. Synchronization resistance
Supply Voltage
The integrated circuit U217B (which also contains
internal voltage limiting) can be connected via the diode
(D1) and the resistor (R1) with the mains supply. An
internal climb circuit limits the voltage between Pin 5 and
7 to a typical value of 9.25 V.
0
03
69
Itot ( mA )
12
Figure 7. Maximum resistance of R1
15
6
VMains=230VX
5
4
3
2
1
0
03
69
Itot ( mA )
12
Figure 8. Power dissipation of R1
according to current consumption
15
Rev. A4, 23-Feb-01
3 (11)

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U217B
Absolute Maximum Ratings
Reference point Pin 7
Parameters
Supply current
Sync. current
Output current ramp generator
Input voltages
Power dissipation
Tamb = 45°C
Tamb = 100°C
Junction temperature
Operating ambient temperature range
Storage temperature range
Pin 5
Pin 8
Pin 1
Pin 1, 3, 4, 6
Pin 2
Pin 8
Symbol
–IS
ISync.
IO
–VI
–VI
±VI
Ptot
Ptot
Tj
Tamb
Tstg
Value
30
5
3
VS
2 to VS
7.3
400
125
125
0 to 100
–40 to + 125
Unit
mA
mA
mA
V
V
V
mW
mW
°C
°C
°C
Thermal Resistance
Junction ambient
Parameters
Symbol
RthJA
Value
200
Unit
K/W
Electrical Characteristics
–VS = 8.5 V, Tamb = 25°C, reference point Pin 7, unless otherwise specified
Parameters
Test Conditions / Pin
Supply-voltage limitation –IS = 5 mA
Supply current
Pin 5
Pin 5
Voltage limitation
Synchronous current
I8 = ± 1 mA
Pin 8
Pin 8
Zero detector
Output pulse width
Output pulse current
VM= 230 V,
Rsync = 220 kW
Rsync = 470 kW
V6 = 0 V
Pin 6
Comparator
Input offset voltage
Pin 3,4
Input bias current
Pin 4
Common-mode input
voltage
Pin 3,4
Threshold internal
reference
V3 = 0 V
Pin 4
Ramp generator, Pin 1, figure 1
Period
Final voltage
–IS= 1 mA, Isync =1 mA,
C1 = 100 mF, C2 = 1 mF,
R4= 100 kW
Initial voltage
Charge current
V2 = 0 V, I8 = –1 mA Pin 2
Symbol
–VS
–IS
± VI
±Isync
±Isync
tP
tP
–IO
VI0
IIB
–VIC
–VT
T
V1
V1
–I2
Min.
8.6
7.5
0.12
100
1
0.9
6.8
13
Typ. Max. Unit
9.25 9.9
V
500 mA
8.7 V
mA
35 mA
260 ms
460 ms
mA
5 15 mV
1 mA
(VS–1)
V
1.25 V
1.5 s
1.40 1.80
V
7.3 7.8 V
17 26 mA
4 (11)
Rev. A4, 23-Feb-01

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Applications
L
RL
Load
VM = 230 V ~
N VDR
U217B
270 kW
56 W
1N4007
18 kW
1.5 W
8765
U217B
+5 V
CNY21
1234
56 kW
47 mF/
10 V
39 kW
II  1.5 mA
VI
Figure 9. Power switch
2.2 mF/
10 V
C2
220 kW
(250 V~)
R2
(Rsync)
D1 1N4007
R1
18 kW/
2W
R8
470 kW
NTC/M87
B value =
3988
BC237
R(25)
R6
100 kW 100 kW
R4
100 kW
1)
R5
1
3
R9
150 W
4
Rp
220 kW
R7
130 kW
2
Ramp
generator
8
Synchronization
5
Supply
7
+
+
Full-wave logic
Comparator
6
Pulse
amplifier
Reference voltage
1.25 V
U217B
Load
1000 W
L
C1
VM =
230 V~
100 W
R3
N
R(25) =100 kW/B =3988
Figure 10. Temperature control 15 to 35°C with sensor monitoring
NTC–Sensor M 87 Fabr. Siemens
R(15) = 159 kW
R(35) = 64.5 kW
R51) determines the proportional range
Rev. A4, 23-Feb-01
5 (11)