Dual Channel Voltage-to-Current (V-I) converter circuit with BJT

Rajkumar Sharma
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SKU: EL154054
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This low-side voltage-to-current (V-I) converter delivers a well-regulated current to a load. The circuit accepts an input voltage from 0V to 3V and converts it to a current from 0A to 6A (combined). The current is accurately regulated by feeding back the voltage drop across a low-side current-sense resistor (R8, R9 + R16, R17) to the OPAMP. Resistor divider (R4 and R5 + R12 and R13) is implemented to limit the maximum voltage at the non-inverting input, Vin, and sense resistor, (R8, R9 + R16, R17), at full-scale. Using a Darlington BJT reduces the output current requirement for the OPAMP. Feedback components R6+R13, R7+R15, and C5+C6 provide compensation to ensure stability. R6+R13 isolates the input capacitance of the bipolar junction transistor (BJT) R7+R15 provides a DC feedback path directly at the current setting resistor (R8, R9 + R16, R17), and C5+C6 provides a high-frequency feedback path that bypass the BJT.

The project is built using the OPA2170 dual OPAMP, which enables the creation of two separate channels. Each channel is capable of handling a current of up to 3A, and when combined, they provide a total current of 6A. Users have the flexibility to utilize only one channel if a lower current is required, in which case the components associated with the second channel can be omitted. To achieve a 6A load, simply tie inputs A1 and A2 together. For a 3A load, only one input is necessary.

Note: To effectively manage the excessive heat generated by the BJT, it is recommended to utilize a large-sized heat sink. Additionally, it is advisable to employ a fan to facilitate efficient power dissipation. Mount Q2 and Q4 on big heatsink, Q1 and Q3 can be mounted on a small heatsink.

Features

Input Power Supply Range 12V to 30V DC
Load 5Amps (3A + 3A)
Input Voltage 0 to 3V
4 x 4 mm Mounting Holes
On Board Power LED
PCB Dimensions 91.44 x 36.20 mm

Connections

CN1: Pin 1 = Power Supply Input 12V TO 30V, Pin 2 = GND
CN2: Pin 1 = +Load, Pin 2 = -Load
CN3: Pin 1 = No Use, Pin 2 = Analog Voltage in for Channel A1, Pin 3 = GND
CN4: Pin 1 = No Use, Pin 2 = Analog Voltage in for Channel A2, Pin 3 = GND
D1: Power LED

Schematic

Parts List

NO.	QNTY.	REF.	DESC.	MANUFACTURER	SUPPLIER	SUPPLIER PART NO
1	2	CN1,CN2	2 PIN SCREW TERMINAL PITCH 5.08MM	PHOENIX	DIGIKEY	277-1247-ND
2	2	CN3,CN4	3 PIN MALE HEADER PITCH 2.54MM	WURTH	DIGIKEY	732-5316-ND
3	2	C1,C2	220uF/35V	RUBYCON	DIGIKEY	1189-35SGV220M10X10.5CT-ND
4	4	C3,C4,C7,C8	100nF/50V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
5	2	C5,C6	1nF/50V CERAMIC SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
6	6	R3,C9,R10,C10,R11,R18	DNP
7	1	D1	LED RED SMD SIZE 0805	LITE ON INC	DIGIKEY	160-1427-1-ND
8	2	Q1,Q3	TIP41 TO220	ST	DIGIKEY	497-2622-5-ND
9	2	Q2,Q4	TIP35C TO247	ST	DIGIKEY	497-2609-5-ND
10	2	R1,R19	7.5K 5% SMD SIZE 1206	YAGEO/MURATA	DIGIKEY
11	1	R2	1E 5% SMD SIZE 1206	YAGEO/MURATA	DIGIKEY
12	2	R4,R12	100K 1% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
13	2	R5,R14	5.23K 1% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
14	2	R6,R13	100E 5% SMD SIZE 1206	YAGEO/MURATA	DIGIKEY
15	2	R7,R15	10K 5% SMD SIZE 0805	YAGEO/MURATA	DIGIKEY
16	4	R8,R9,R16,R17	0.1E 1% 3W SMD SIZE 2512	BOURNS	DIGIKEY	CRA2512-FZ-R100ELFCT-ND