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Original question:

TIDA-01505: TIDA-01505

TIDA-01505: Start up circuit

Smitha M S
Prodigy 250 points
Part Number: TIDA-01505

Hello,
Had query on Active Startup circuit:
1. STP03D200 BJT has minimum  hfe value of 230 and 200 for Ic=20mA and 30mA, why is the assumed hfe value is 500?
2. Rstart_slow value calculated tells it should be <150Mohm, But the value selected is 6 instances of 1.5Mohm which comes to around 9Mohm. Let me know the reason for selecting so low value

  • 0
    TI__Mastermind 18121 points

    Hi Smitha,

    When Ic decreases, the BJT hFE increases, the datasheet doesn't specify hFE at all conditions therefore it takes the assumption here.

    The lower the start up resistance, the faster the circuit starts up. Placing 150M Ohm will take long time to startup.