Chuck Visedo
New Member
hey guys:
Any transistor guns out there ??
i have been trying to design a h-bridge using BJT transistors to operate a DC motor at 48 volts. The control circuit is already finished. I am using/ well plan to use, a microcontroller with pulse width modulation to control the speed of the motor. But i cant get my H-bridge to work at all! in particular i have almost no idea in working out the Resistor values of my bridge.
I have posted a picture of the design. if anyone can step me through the design process it would be much appreciated.
Heres what i have done so fare. :
given that i want to run 48 volts to the motor but which to switch it on with a 5b high from the micro controller, i have chosen 4 darlington pairs! BDX54B and BDX54C, these npn and pnp transistors have a Vceo of 80 volts! so i know they are a good choice. furthermore they have a Hfe minimum value of 750.
for the Motor that we are running i calculated the Stall current to be 10 Amps. so from this i worked out that i need ten amps in the collector of the top left transistor (on the drawing) therefore i calculated R2 to be
(48-0.4-1.7)/R2=10ma (given the Ib Ic relationship) hence R2 to be 4.6k is this right ?? if not how do i calculate the resistor values throughout the circuitry to get it to work ??
the idea is to have four output pins of the microcontroller which sends 5v high (20mA) or a 0 and in that way engage forward and revers for the motor!!
the bottom transistors i'm using are BC109s though i think there not suitable given that only have a vceo of 45
can anyone help me ??
Any transistor guns out there ??
i have been trying to design a h-bridge using BJT transistors to operate a DC motor at 48 volts. The control circuit is already finished. I am using/ well plan to use, a microcontroller with pulse width modulation to control the speed of the motor. But i cant get my H-bridge to work at all! in particular i have almost no idea in working out the Resistor values of my bridge.
I have posted a picture of the design. if anyone can step me through the design process it would be much appreciated.
Heres what i have done so fare. :
given that i want to run 48 volts to the motor but which to switch it on with a 5b high from the micro controller, i have chosen 4 darlington pairs! BDX54B and BDX54C, these npn and pnp transistors have a Vceo of 80 volts! so i know they are a good choice. furthermore they have a Hfe minimum value of 750.
for the Motor that we are running i calculated the Stall current to be 10 Amps. so from this i worked out that i need ten amps in the collector of the top left transistor (on the drawing) therefore i calculated R2 to be
(48-0.4-1.7)/R2=10ma (given the Ib Ic relationship) hence R2 to be 4.6k is this right ?? if not how do i calculate the resistor values throughout the circuitry to get it to work ??
the idea is to have four output pins of the microcontroller which sends 5v high (20mA) or a 0 and in that way engage forward and revers for the motor!!
the bottom transistors i'm using are BC109s though i think there not suitable given that only have a vceo of 45
can anyone help me ??