Hi guys, I designed a simple circuit here to use an Arduino Pro mini controlling a heater rod for my personal project. My heater rod is rated at 24V, 25W. I'm controlling the heater rod using a BJT transistor, FMMT617TA which is some leftover parts from my previous project.
After I got my circuit board designed and made, I only realized that the FMMT617A has a Collector-Emitter Breakdown Voltage (BVceo) of 15VDC when I'm doing testing. To my surprise, everything seems to be working fine. My arduino pin 11 is giving 3.7V, I'm measuring Vce = 2.7V, voltage across heater = 20.9V, current draw of circuit is at 1.1A. I was expecting that the FMMT617TA transistor would be burnt, as I'm applying 24VDC to drive the circuit.
I'm confused here. My understanding is BVceo is actually the maximum allowable voltage that can be used for the transistor to control the load, and normally we should always chose a transistor that has BVceo > system voltage (for this case, I should be using a transistor with BVceo > 24VDC). So did I misunderstood the interpretation of BVceo?
After I got my circuit board designed and made, I only realized that the FMMT617A has a Collector-Emitter Breakdown Voltage (BVceo) of 15VDC when I'm doing testing. To my surprise, everything seems to be working fine. My arduino pin 11 is giving 3.7V, I'm measuring Vce = 2.7V, voltage across heater = 20.9V, current draw of circuit is at 1.1A. I was expecting that the FMMT617TA transistor would be burnt, as I'm applying 24VDC to drive the circuit.
I'm confused here. My understanding is BVceo is actually the maximum allowable voltage that can be used for the transistor to control the load, and normally we should always chose a transistor that has BVceo > system voltage (for this case, I should be using a transistor with BVceo > 24VDC). So did I misunderstood the interpretation of BVceo?
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